[repost]Neither existence nor non-existence of the ORIGIN OF THE WORLD,
two analyses of a question left un-answered by the Buddha.

Causality requires a cause, an effect (distinct from the cause) and a causal relationship (neither the cause nor the effect); a causal relationship is itself dependent on conditions (or 'context'): a given remark may lead to confusion or to an insight, some given food may lead to saving a life or ending it (e.g. due to allergic reaction), et cætera.
In a common sense, the primordial origin of the world would be unique, alone, isolated, and the first and only cause of future evolutions.

First analysis:

We may imagine that the 'context' of the first causal step is simply the origin, i.e. the 'cause.' This would be different from commonly-found 'contexts' but the origin is clearly a special situation so why not?

The first causal step, like any other, depends on a 'causal' relationship distinct from the origin itself. Such a causal relationship needs to pre-exist the step ('pre-exist' "in dependence" or "in causality," not necessarily in time): the causal relationship cannot arise between the origin and the first step because such an arising would simply become the first step itself and would need its own causal relationship… ad infinitum. So, the causal relationship cannot arise after the origin.
Moreover, by the definition of origin, the causal relationship cannot exist before the origin either…
So both origin and the first causal relationship have to co-arise.

However, how could both the 'origin' and something else co-exist, and the 'origin' still be considered the origin? The origin of the world surely has to include everything which exists, so it seems a new 'extended' origin should be defined, consisting of the previously considered 'origin' and the first causal relationship…
But such an extended origin should then kick-start the evolution, which is itself a first causal step, which requires a causal relationship, which requires an 'extended extended' origin… ad infinitum.

Second analysis:

Causality requires a cause, an effect (distinct from the cause) and a causal relationship (neither the cause nor the effect).

One should see that the co-arising of a causal relationship and its associated effect requires the co-arising of the associated cause too, for if the effect did arise even though its cause did not exist, how could the causal relationship really be causal?
But one should also see that a causal relationship co-arises with the associated effect, for if the effect did not arise even though the cause and the causal relationship were present, how could the causal relationship really be causal?
And if the causal relationship did not co-exist, why would two unrelated situations be called the 'cause' and the 'effect'?
So the origin, the causal relationship, and the first step away from the origin have to co-arise…

However, how could both the 'origin' and something else co-exist, and the 'origin' still be considered the origin? The origin of the world surely has to include everything which exists, so it seems a new 'extended' origin should be defined… ad infinitum again!

Emptiness (or conventionality)

Is causality —as we access it— just story-making?

Causality —as we access it— does not exist in and of itself. We knew as much as soon as we accepted that a context matters. But more fundamentally, causality requires distinction between a cause, an effect, a relationship… i.e. it basically requires a consciousness distinguishing / identifying these, and then tying them back together.
The tie is mind-made: causality is a fiction we explain the world with. Causality is conventional.
That causality is conventional is why we so often get it wrong: causality breaks every time we are blind to some element of the context that turns out to be necessary for the story to make sense. We then adjust the story to include said element… until the next time it breaks.

Our stories don't need to dramatically change from one instant to the next though, so there is some stubborn 'real' causality out there. The context of causal relationships does not dramatically change from one instant to the next, the stubbornness of reality is a form of inertia. We do not have access to any 'real' causality though, no more than seeing a star allows us to know for sure that no dramatic event affected it during the time it took for its light to reach our eye. Causality, as we commonly define it, would not depend on whether a conscious observer is present or not; it would not depend on the labelling of what is cause and what is effect; it could not be confused with 'correlation'… Causality, as we commonly define it, cannot be what really is the evolution of the processes constitutive of reality.

Wrap-up

The Buddha asserted neither the existence nor the non-existence of the origin of the world. He merely stated that moving up the causal chain led to an infinite regress (as we have seen above), and thus that the origin could not be found. Searching for the origin of the world is a waste of time when it comes to getting free from suffering.

We have seen that the origin of the world may only be out of causality, but then why would we call it the 'origin' in the first place? Another situation should be identified as the first cause and be called the "causal origin" instead…

Causality —as we access it— is conventional. The definition of Origin is conventional too. Our difficulty is that both conventions are incompatible! A "causal origin" cannot exist any more than a "childless parent": two sensical words don't automatically make sense together.

The video TEDxParis 2011 - Etienne Klein - Peut-on penser l'origine de l'Univers ? is about "can we conceive the origin of the Universe?" and addresses the claim that there must be a creator from a "cosmological physics" perspective (Big Bang, etc). Turn the subtitles on! This is very accessible and might be instructive if you don't follow physics too closely.